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Documentation

Find information, examples, FAQs and extensive descriptions of the data, curated by the survey teams.

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GALAH

The Galactic Archaeology with HERMES survey is collecting stellar parameters and abundances for one million stars in the Milky Way. GALAH yields a comprehensive view of the formation & evolution of the Galaxy.
Nov. 6, 2020 by J. Simpson
April 20, 2021, 4:35 p.m. J. Simpson

Spectra Data Access

GALAH DR3

Description of the spectral data

GALAH DR3 provides reduced one-dimensional spectra for each star in the main catalogue. For each star there are (up to) four files, one for each HERMES camera. The entire GALAH DR3 spectral catalogue consists of 2,342,026 FITS files.

For a given star on a given camera, each file contains five extensions:

Element Name Description
0 PRIMARY Unnormalised spectrum with sky subtraction
1 input_sigma Variance of the unnormalised spectrum with sky subtraction. This is expressed as the percentage of the unnormalised flux.
2 no_sky_subspectrum Unnormalised spectrum with no sky subtraction
3 no_sky_sigma Variance of the unnormalised spectrum with no sky subtraction
4 normalised spectra Pseudo-continuum normalised spectrum with sky subtraction

The naming convention of the spectra files is the sobject_id of a star followed by the camera number (i.e., 1=blue, 2=green, 3=red, 4=near-infrared). So, for example, for sobject_id 170418003701205, there are four files: 1704180037012051.fits, 1704180037012052.fits, 1704180037012053.fits, 1704180037012054.fits.

Missing spectral data

There are 12181 stars which are missing the spectra for some of their cameras. We provide a file at GALAH_DR3_list_missing_reduced_spectra_v2.csv that lists the sobject_id and the missing cameras.

The missing spectra are concentrated into two data ranges:

  • On the night of 27 August 2015 two fields (field_id 64 and 287) had data reduction problems that resulted in their spectra not being properly ingested into the Data Central system. This means that for sobject_id starting with 1508270040 or 1508270052, there are 243 and 111 stars respectively missing spectra for the blue and sometimes green camera.
  • For the nights of 21-26 December 2018 (i.e., all sobject_id starting with 181221, 181222, 181223, 181224, 181225, 181226) there was a fault with the infrared camera of HERMES. This means that all stars observed on those nights lack a spectral file ending with 4.
    • For 227 stars of the stars observed on these nights, their spectrum files do not have the fifth extension described above – the normalized spectrum. We provide a file at GALAH_DR3_list_missing_normalized_spectra_v2.csv that lists the sobject_id of these files.


Acquiring the spectral data

On this page we describe three methods for acquiring the spectra depending on your requirements:

  1. A few stars
  2. A larger number of stars
  3. The entire GALAH spectral catalogue.


(1) Downloading the spectra for a few stars

The spectrum of an individual star can be accessed via the Single Object Viewer (Located inder the "Services" menu).

Search for the sobject_id of a given star, e.g., 170418003701205, and click on the entry that appears in the drop-down menu:



SOV GALAH Example 1


On the results pages, you can view the spectrum of the star:


SOV GALAH Example 2


You can then either download all the available spectrum files for this sobject_id using the "Download all data products" button at the top-right of the page, or download the spectrum from an individual camera.


SOV GALAH Example 3

GALAH SOV Example 4


(2) Downloading the spectra for a larger number of stars

If you would like the spectra for a large number of stars, this can be achieved using the Bulk Download (Located inder the "Services" menu). A rule-of-thumb is that the query to create the packaged tar.gz file of spectra will take about 10 minutes per 10000 sobject_id requested.

You will require the list of sobject_id you are interested in. In this example, we select those by identifying likely members of the globular cluster omega Centauri using the Catalogue Query service:

SELECT
   sobject_id
   FROM galah_dr3.main_star
   WHERE 
      1=CONTAINS(POINT('ICRS', ra, dec),
                 CIRCLE('ICRS', 201.6836, -47.5068, 1.0 ))
   AND sqrt(power(pmra-(-3.2),2)+power(pmdec-(-6.9),2)) < 1.5
   AND rv_galah > 170

This will return a list of 341 sobject_id.


Bulk Downloader Example 1


The Bulk Download facility requires the sobject_id to be in a comma-separated single-line list. This will need to be done with your favourite text editor or bash command.

Once you have the list correctly formatted, copy-and-paste it into the Source List box, select GALAH Data Release 3 as the Data Release, and GALAH DR3 HERMES 1D Spectrum as the Data products: Spectra.

Click Submit to start the query.


Bulk Downloader GALAH Example 4


For a query of this size, the process of packaging the spectra will take about a minute.

On completing the query, you will be presented with a results page that looks like this:


GALAH Bulk Download Example 5


The spectra can then be downloaded using either link on the right of the page. These links can also be used with a command line function such as wget.


(3) Downloading the entire GALAH spectral catalogue

CAUTION: This is possible using the bulk download option described above, but the query takes about 20 hours to complete. Do not do this.

The entire GALAH DR3 spectral library can be found here. This is split over two files: one file for the 588,343 stars that were successfully normalized, and one file of the 227 stars that were not successfully normalised (discussed above in the section "Missing spectral data" and listed at GALAH_DR3_list_missing_normalized_spectra_v2.csv). As described above, 12181 stars are missing spectra for one or two of their cameras due to reduction or instrumentation problems. A list of these missing spectra can be found in GALAH_DR3_missing_reduced_spectra_v2.csv.

On decompression, you will require about 385 GB of free space. The decompressed files are located in a single directory, so please be aware of any file management limitations you might have dealing with 2 million files in a single directory.

Filename Number of stars Number of FITS files Size Description
GALAH_DR3_all_spectra_with_normalisation_v2.tar.gz 588,343 2341345 228 GB GALAH DR3 spectral files that have been continuum normalised
GALAH_DR3_all_spectra_missing_normalisation_v2.tar.gz 227 681 49M GALAH DR3 spectral files that lack continuum normalisation

The two files can be downloaded with the following wget command (removing the --spider flag):

# Remove --spider to download
# Download the spectra for 588,343 stars that were successfully normalised.
wget --spider https://cloud.datacentral.org.au/teamdata/GALAH/public/GALAH_DR3/spectra/GALAH_DR3_all_spectra_with_normalisation_v2.tar.gz
# Download the spectra for 227 stars that were not normalised
wget --spider https://cloud.datacentral.org.au/teamdata/GALAH/public/GALAH_DR3/spectra/GALAH_DR3_all_spectra_missing_normalisation_v2.tar.gz
Nov. 6, 2020 by J. Simpson
April 20, 2021, 4:35 p.m. J. Simpson